Murder is the crime of intentionally causing the death of another human being, without lawful excuse. When an illegal death was not caused intentionally, but was caused by negligence (or some other defense, such as diminished capacity), the crime committed is manslaughter, which is considered to be less serious than murder. Manslaughter is often broken into two categories: involuntary manslaughter and voluntary manslaughter.

A difficult issue in defining murder is what counts as causing death. It is impossible to give a precise definition of this, but some legal principles have been developed to help. For example, many common law jurisdictions abide by the year and a day rule, which provides that one is to be held responsible for a person's death only if they die within a year and a day of the act. Thus, if you seriously injured someone, and they died from their injuries within a year and a day, you would be guilty of murder; but you would not be guilty if they died from their injuries after a year and a day had passed.

It is not murder to kill someone with lawful excuse; lawful excuses include killing enemy combatants in time of war (but not after they surrendered), killing a person who poses an immediate threat to the lives of ones self or others (i.e., in self-defence), and executing a person in accordance with a sentence of death (in those jurisdictions which retain capital punishment). Sometimes extreme provocation or duress can justify killing another as well. These cases of killing are called justifiable homicide[?].

Under English law (and the law of other countries, such as Australia, which pay close heed to the decisions of British courts), it is murder to kill another human being for food, even if without doing so one would die of starvation. This originated in a case of three shipwrecked sailors cast adrift off the coast of South Africa in the 1920s; two of the sailors conspired to kill the other sailor, and having killed him ate his flesh to survive.

Most countries allow conditions that "affect the balance of the mind" to be regarded as mitigating circumstances against murder. This means that a person may be found guilty of "manslaughter on the basis of diminished responsibility" rather than murder, if it can be proved that they were suffering from a condition that affected their judgement at the time. Depression, Post-traumatic stress disorder and medication side-effects are examples of conditions that may be taken into account when assessing responsibility.

Canada has about 550 murders per year, a number that is steadily decreasing. This is equivalent to numbers in most of the western world, except the U.S. which has triple the number per capita. The main methods of murder in Canada are shootings (30%), stabbings (30%), and beatings (22%).

Canada has four types of crime that can be considered muder:

first degree murder

second degree murder

manslaughter

infanticide

For every murder in Canada there are about 1.5 attempted murders.

About one in three Canadian murders are committed by a family member. One in eight is gang related. About 80% of murderers in Canada are caught within a year.

(All statistics are from the 2001 census)

The United States
In the United States the term First-degree murder refers to murder which is planned in advance. Second-degree murder refers to murder which was unplanned. Third-degree murder is also known as manslaughter.
In order for a defendant to be convicted of first-degree murder, US law requires proof of the following 4 elements:

Felony Murder Statutes
Many jurisdictions in the United States have adopted felony murder statutes[?], according to which anyone who commits a serious crime (a felony), which results in a person's death, is guilty of murder. This applies even if one is not actually responsible for the person's death; for example, a driver for an armed robbery can be convicted of murder if one of the robbers killed someone in the process of the robbery, even though the driver was not (directly, at least) responsible for this person's death.